It is known in the absorption refrigeration art relating to systems wherein evaporation of liquid refrigerant takes place in the presence of a non-condensible inert gas that a lower evaporator temperature can be effected by precooling the liquid refrigerant before it passes to the main or low temperature evaporator. As an example, U.S. Pat. No. 2,167,697 describes a system in which the refrigerant is ammonia, the absorption liquid is water and the non-condensible inert gas is hydrogen. The hydrogen flows from the absorber and is divided into two streams. One stream after being cooled flows to the main or low temperature evaporator where it passes in direct contact with liquid ammonia which is vaporizing. From the evaporator the mixture of ammonia gas and hydrogen returns to the absorber. The other stream of hydrogen after being cooled flows to a precooler where it passes in direct contact with warm liquid ammonia from the condenser. Since the partial vapor pressure of ammonia in the gas mixture in the precooler is less than the vapor pressure of the warm liquid ammonia entering the precooler from the condenser some of the liquid ammonia evaporates and diffuses into the gas mixture with the result that heat is removed from the liquid ammonia. The gas mixture then returns to the absorber. The precooling of the liquid ammonia provides a lower temperature in the evaporator and effects other advantages discussed in the patent.
A subsequent U.S. Pat. No. 3,464,221, describes a refrigeration system embodying the above-summarized concepts and including modifications which control the hydrogen flow in the system. In one embodiment described in this patent the conduit which passes the mixture of hydrogen and ammonia gas from the precooler back to the absorber includes a portion of reduced cross-section which produces a flow restriction, i.e. control of inert gas is effected after the gas leaves the precooler. In another embodiment described in this patent the conduit which conducts liquid refrigerant from the condenser to the precooler is flattened along a portion of its length to avoid undesirable circulation of hydrogen over the free liquid level in this conduit.
The present invention provides an absorption refrigeration system of the above type having an improved form of inert gas control. In this system control of the inert gas is effected before the gas enters the precooler in that the inert gas stream from the absorber is acted on by a flow restriction located between the low temperature evaporator and the non-condensible gas inlet of the precooler. Preferably the flow restriction is a slotted orifice which passes a portion of the gas into the cooler and which directs the remainder into the low temperature evaporator.